by PhilipJ on 20 October 2009

Our bodies use a lot of energy. ATP (adenosine triphosphate) is one of the major currencies of energy in our cells; it is continually used and rebuilt throughout the day. Amazingly, if you add up the amount of ATP that is built each day, it would roughly equal the weight of your entire body. This ATP is spent in many ways: to power muscles, to make sure that enzymes perform the proper reactions, to heat your body. The lion’s share, however, goes to the protein pictured here: roughly a third of the ATP made by our cells is spent to power the sodium-potassium pump.

The sodium-potassium pump (PDB entries 2zxe and 3b8e) is found in our cellular membranes, where it is in charge of generating a gradient of ions. It continually pumps sodium ions out of the cell and potassium ions into the cell, powered by ATP. For each ATP that is broken down, it moves 3 sodium ions out and 2 potassium ions in. As the cell is depleted of sodium, this creates an electrical gradient and a concentration gradient, both of which are put to use for many tasks.

The most spectacular use of this gradient is in the transmission of nerve signals. Our nerve axons deplete themselves of sodium ions, then use special voltage-gated sodium channels to allow the ions to rush back in during a nerve impulse. The sodium-potassium pump has the job of keeping the axon ready for the next signal. The gradient also helps control the osmotic pressure inside cells, and powers a variety of other pumps that link the flow of sodium ions with the transport of other molecules, such as calcium ions or glucose.